diff --git a/scrapy/http/request/__init__.py b/scrapy/http/request/__init__.py
index 65355b03d..187238b1c 100644
--- a/scrapy/http/request/__init__.py
+++ b/scrapy/http/request/__init__.py
@@ -96,8 +96,9 @@ class Request(object_ref):
         """Return a copy of this Request"""
         return self.replace()
 
-    def replace(self, url=None, callback=None, method=None, headers=None, body=None, 
-                cookies=None, meta=None, encoding=None, dont_filter=None):
+    def replace(self, url=None, callback=None, method=None, headers=None, body=None, \
+                cookies=None, meta=None, encoding=None, priority=None, \
+                dont_filter=None, errback=None):
         """Create a new Request with the same attributes except for those
         given new values.
         """
@@ -109,4 +110,6 @@ class Request(object_ref):
                               cookies=self.cookies if cookies is None else cookies,
                               meta=self.meta if meta is None else meta,
                               encoding=self.encoding if encoding is None else encoding,
-                              dont_filter=self.dont_filter if dont_filter is None else dont_filter)
+                              priority=self.priority if priority is None else priority,
+                              dont_filter=self.dont_filter if dont_filter is None else dont_filter,
+                              errback=errback)
diff --git a/scrapy/tests/test_http_request.py b/scrapy/tests/test_http_request.py
index 08fe70edf..c0ae0cab5 100644
--- a/scrapy/tests/test_http_request.py
+++ b/scrapy/tests/test_http_request.py
@@ -2,6 +2,7 @@ import cgi
 import weakref
 import unittest
 import xmlrpclib
+from inspect import getargspec
 from cStringIO import StringIO
 from urlparse import urlparse
 
@@ -170,6 +171,13 @@ class RequestTest(unittest.TestCase):
         self.assertEqual(r4.meta, {})
         assert r4.dont_filter is False
 
+        # __init__ and replace() signatures must be equal unles *args,**kwargs is used
+        i_args, i_varargs, i_varkwargs, _ = getargspec(self.request_class.__init__)
+        self.assertFalse(bool(i_varargs) ^ bool(i_varkwargs))
+        if not i_varargs:
+            r_args, _, _, _ = getargspec(self.request_class.replace)
+            self.assertEqual(i_args, r_args)
+
     def test_weakref_slots(self):
         """Check that classes are using slots and are weak-referenceable"""
         x = self.request_class('http://www.example.com')